Zeolites are synthesized from a reaction mixture by means of hydrothermal crystallization. A reaction mixture is prepared by mixing suitable proportions of the required reactants in order to obtain the aimed zeolite type. When this mixture is heated, at the end of certain periods of time, nuclei of the zeolite crystals are formed and then the crystals start to grow. When there is a substrate in the medium immersed in the reaction mixture, the nuclei/crystals often chemically bind with this substrate and form a zeolite coating which is strongly attached thereon. Properties of this coating depend on the composition of the reaction mixture that is used, and the experimental conditions such as reaction temperature and time and mixing. Use of dilute solutions as the reaction mixture instead of highly viscous gels used in conventional zeolite synthesis has a positive impact on the coating quality.
Since zeolites are metastable materials, a zeolite phase synthesized from a reaction composition transforms into other phases after longer reaction times. This situation impedes the coatings from being sufficiently thick when the conventional single step synthesis method is used for many zeolite phases. In cases where metastable phase transformation does not occur, since composition of the solution changes as the time increases, as a result of the crystallization activity in the reaction solution, preparing a thick coating is still not easy. Multi-step methods that may be used for preparation of thick coatings are not practical or economical. Additionally, strength of the thick coatings is also low when these methods are used and the coatings have a very compact structure that will make diffusion difficult.
In the method of direct heating of the substrate by conduction, wherein the substrate is heated by the help of a resistance (one of the state-of-the-art applications), the reaction solution is kept at a temperature that is lower than the reaction temperature by the help of a water bath. In this manner, phase transformation of the zeolite is delayed for long periods of time and thus thicker coatings can be obtained in comparison to the conventional methods. These coatings also have an open structure, high diffusion coefficient and relatively higher stability which are necessary for many applications, especially for adsorption heat pump applications.
There are several articles in the literature related to direct heating of the substrate materials by using the method of heating by conduction: “Erdem-Senatalar, A., Tatlier, M., Urgen, M., “Preparation of Zeolite Coatings by Direct Heating of the Substrates”, Microporous and Mesoporous Materials, 32(3), 331-343 (1999)”; “Tatlier, M., Erdem-Senatalar, A., “The Stability of Zeolite Coatings Grown on Metal Supports for Heat Pump Applications”, Studies in Surface Science and Catalysis, Vol. 125, Elsevier, Amsterdam, 101-108 (1999)”; “Tatlier, M., Tantekin-Ersolmaz, S. B., Erdem-Senatalar, A., “Diffusivities of Zeolite Coatings”, (Proc. 13th International Zeolite Conference, 2001, Montpellier, France), A. Galarneau, F. Di Renzo, F. Fajula, J. Vedrine (ed.), Studies in Surface Science and Catalysis, Vol. 135, Elsevier, Amsterdam, 3249-3256 (2001)”; “Erdem-Senatalar, A., Oner, K., Tatlier, M., “Searching for Clear Solution Compositions by Using the Substrate Heating Method”, Studies in Surface Science and Catalysis, Vol. 154 part A-C, 667-670 (2004)”; “Tatlier, M., Erdem-Senatalar, A., “Estimation of the Effective Diffusion Coefficients in Open Zeolite Coatings”, Chemical Engineering Journal, 102(3), 209-216 (2004)”; “Tatlier, M. Demir, M., Tokay, B., Erdem-Senatalar, A., Kiwi-Minsker, L., “Substrate Heating Method for Coating Metal Surfaces with High-Silica Zeolites: ZSM-5 Coatings on Stainless Steel Plates”. Microporous and Mesoporous Materials, 101(3), 374-380 (2007)”; Schlabel, L., Tatlier, M., Schmidt, F., Erdem-Senatalar, A., “Adsorption Kinetics of Zeolite Coatings Directly Crystallized on Metal Supports for Heat Pump Applications”, Applied Thermal Engineering, 30(11/12), 1409-1416 (2010)”.
International patent document no. WO02010120738, an application known in the art, discloses a method of coating a metal surface with a protective metal coating having a lower melting point. After the surface to be coated is heated up to the melting point of the metal coating in a high frequency induction heater, the molten metal coating is immediately applied on the heated surface.
Chinese Patent document no. CN101754508, an application known in the art, discloses an induction heater used for coating steel surfaces. The system includes independent induction heaters and on the upper parts thereof copper coils. Water nozzles are provided at the head ends and the tail ends of the induction coils. The said heater has a simple structure and a high efficiency.
Japanese patent document no. JP2006256066, an application in the state of the art, discloses a method for coating the surface of a substrate with a resin. During coating, the resin acquires the shape of the surface and this shape can be maintained. In the contact process used in the method, the material containing a thermoplastic resin is ensured to contact the surface of the conductive substrate. Then temperature of the substrate surface is increased by means of the induction heater.